MicroRNA control of muscle development and disease

IGF-II is regulated by microRNA-125b in skeletal myogenesis

miR-125b is identified as a myogenic miRNA that regulates skeletal muscle differentiation by targeting IGF-II under the control of mTOR signaling.

MicroRNAs (miRNAs) have emerged as key regulators of skeletal myogenesis, but our knowledge of the identity of the myogenic miRNAs and their targets remains limited. In this study, we report the identification and characterization of a novel myogenic miRNA, miR-125b. We find that the levels of miR-125b decline during myogenesis and that miR-125b negatively modulates myoblast differentiation in culture and muscle regeneration in mice. Our results identify IGF-II (insulin-like growth factor 2), a critical regulator of skeletal myogenesis, as a direct and major target of miR-125b in both myocytes and regenerating muscles, revealing for the first time an miRNA mechanism controlling IGF-II expression. In addition, we provide evidence suggesting that miR-125b biogenesis is negatively controlled by kinase-independent mammalian target of rapamycin (mTOR) signaling both in vitro and in vivo as a part of a dual mechanism by which mTOR regulates the production of IGF-II, a master switch governing the initiation of skeletal myogenesis.

Application of microRNA in cardiac and skeletal muscle disease gene therapy

MicroRNAs (miRNAs) are a class of small ∼22 nt noncoding RNAs. miRNAs regulate gene expression at the posttranscriptional levels by destabilization and degradation of the target mRNA or by translational repression. Numerous studies have demonstrated that miRNAs are essential for normal mammalian development and organ function. Deleterious changes in miRNA expression play an important role in human diseases. We and others have previously reported several muscle-specific miRNAs, including miR-1/206, miR-133, and miR-208. These muscle-specific miRNAs are essential for normal myoblast differentiation and proliferation, and they have also been implicated in various cardiac and skeletal muscular diseases. miRNA-based gene therapies hold great potential for the treatment of cardiac and skeletal muscle disease(s). Herein, we introduce the methods commonly applied to study the biological role of miRNAs, as well as the techniques utilized to manipulate miRNA expression.

Megarole for microRNA in muscle disease

Deregulation of microRNAs in dystrophic muscle highlights their importance in muscle homeostasis. A recent study in Cell Metabolism (Cacchiarelli et al., 2010) shows that the presence of functional dystrophin is required for NO-dependent nitrosylation of the HDAC2 repressor and subsequent activation of a group of microRNAs required for muscle function.

miR-206 and -486 induce myoblast differentiation by downregulating Pax7

The Pax7 transcription factor is required for muscle satellite cell biogenesis and specification of the myogenic precursor lineage. Pax7 is expressed in proliferating myoblasts but is rapidly downregulated during differentiation. Here we report that miR-206 and -486 are induced during myoblast differentiation and downregulate Pax7 by directly targeting its 3' untranslated region (UTR). Expression of either of these microRNAs in myoblasts accelerates differentiation, whereas inhibition of these microRNAs causes persistence of Pax7 protein and delays differentiation. A microRNA-resistant form of Pax7 is sufficient to inhibit differentiation. Since both these microRNAs are induced by MyoD and since Pax7 promotes the expression of Id2, an inhibitor of MyoD, our results revealed a bistable switch that exists either in a Pax7-driven myoblast state or a MyoD-driven myotube state.

Posttranscriptional mechanisms involving microRNA-27a and b contribute to fast-specific and glucocorticoid-mediated myostatin expression in skeletal muscle

Expression of the antigrowth factor myostatin (MSTN) differs between fast and slow skeletal muscles and is increased in nearly every form of muscle atrophy, but the contribution of transcriptional vs. posttranscriptional mechanisms to its differing expression in these states has not been defined. We show here that levels of mature MSTN mRNA were sixfold greater in fast vs. slow muscle and were increased twofold in fast muscle in response to dexamethasone (Dex) injection in vivo and in C₂C₁₂ myotubes following Dex treatment in vitro, but that levels of MSTN pre-mRNA, a readout of transcription, only minimally and nonsignificantly differed in these states. Moreover, Dex treatment with or without cotransfection with a glucocorticoid receptor expression construct had only modest effects on mouse MSTN promoter activity in C₂C₁₂ myotubes. We therefore explored the potential contribution of posttranscriptional mechanisms, and the role of the microRNAs miR-27a and b in particular, on MSTN expression. The MSTN 3'-untranslated region (UTR) contains a putative recognition sequence for miR-27a and b that is conserved across a wide range of vertebrate species. Cotransfection of a MSTN 3'-UTR-luciferase construct with a miR-27b expression construct significantly attenuated by approximately half while mutation of the miR-27 recognition sequence significantly increased by approximately twofold the activity of a MSTN 3'-UTR construct and decreased mRNA degradation of a luciferase reporter construct in C₂C₁₂ myotubes. Expression of miR-27a and b was almost sixfold greater in slow-twitch than in fast-twitch muscle in vivo, and miR-27a expression was significantly decreased by nearly half by glucocorticoid treatment in vitro. Finally, the miR-27a and b promoters were activated by cotransfection with the slow-specific signaling molecules calcineurin and peroxisome proliferator-activated receptor-γ coactivator-1α. The present data represent the first demonstration that posttranscriptional mechanisms involving miR-27a and b may contribute to fast-specific and glucocorticoid-dependent myostatin expression in muscle.

A network connecting Runx2, SATB2, and the miR-23a~27a~24-2 cluster regulates the osteoblast differentiation program

Induced osteogenesis includes a program of microRNAs (miRs) to repress the translation of genes that act as inhibitors of bone formation. How expression of bone-related miRs is regulated remains a compelling question. Here we report that Runx2, a transcription factor essential for osteoblastogenesis, negatively regulates expression of the miR cluster 23a∼27a∼24-2. Overexpression, reporter, and chromatin immunoprecipitation assays established the presence of a functional Runx binding element that represses expression of these miRs. Consistent with this finding, exogenous expression of each of the miRs suppressed osteoblast differentiation, whereas antagomirs increased bone marker expression. The biological significance of Runx2 repression of this miR cluster is that each miR directly targets the 3' UTR of SATB2, which is known to synergize with Runx2 to facilitate bone formation. The findings suggest Runx2-negative regulation of multiple miRs by a feed-forward mechanism to cause derepression of SATB2 to promote differentiation. We find also that miR-23a represses Runx2 in the terminally differentiated osteocyte, representing a feedback mechanism to attenuate osteoblast maturation. We provide direct evidence for an interdependent relationship among transcriptional inhibition of the miR cluster by Runx2, translational repression of Runx2 and of SATB2 by the cluster miRs during progression of osteoblast differentiation. Furthermore, miR cluster gain of function (i.e., inhibition of osteogenesis) is rescued by the exogenous expression of SATB2. Taken together, we have established a regulatory network with a central role for the miR cluster 23a∼27a∼24-2 in both progression and maintenance of the osteocyte phenotype.

Troponin T isoforms and posttranscriptional modifications: Evolution, regulation and function

Troponin-mediated Ca²(+)-regulation governs the actin-activated myosin motor function which powers striated (skeletal and cardiac) muscle contraction. This review focuses on the structure-function relationship of troponin T, one of the three protein subunits of the troponin complex. Molecular evolution, gene regulation, alternative RNA splicing, and posttranslational modifications of troponin T isoforms in skeletal and cardiac muscles are summarized with emphases on recent research progresses. The physiological and pathophysiological significances of the structural diversity and regulation of troponin T are discussed for impacts on striated muscle function and adaptation in health and diseases.

MicroRNA-1 regulates smooth muscle cell differentiation by repressing Kruppel-like factor 4

The role of microRNA-1 (miR-1) has been studied in cardiac and skeletal muscle differentiation. However, it remains unexplored in vascular smooth muscle cells (SMCs) differentiation. The aim of this study was to uncover novel targets of and shed light on the function of miR-1 in the context of embryonic stem cell (ESC) differentiation of SMCs in vitro. miR-1 expression is steadily increased during differentiation of mouse ESC to SMCs. Loss-of-function approaches using miR-1 inhibitors uncovered that miR-1 is required for SMC lineage differentiation in ESC-derived SMC cultures, as evidenced by downregulation of SMC-specific markers and decrease of derived SMC population. In addition, bioinformatics analysis unveiled a miR-1 binding site on the Kruppel-like factor 4 (KLF4) 3' untranslated region (3'UTR), in a region that is highly conserved across species. Consistently, miR-1 mimic reduced KLF4 3'UTR luciferase activity, which can be rescued by mutating the miR-1 binding site on the KLF4 3'UTR in the reporter construct. Additionally, repression of the miR-1 expression by miR-1 inhibitor can reverse KLF4 downregulation during ESC-SMC differentiation, which subsequently inhibits SMC differentiation. We conclude that miR-1 plays a critical role in the determination of SMC fate during retinoid acid-induced ESC/SMC differentiation, which may indicate that miR-1 has a role to promote SMC differentiation.

The expression of myogenic microRNAs indirectly requires protein arginine methyltransferase (Prmt)5 but directly requires Prmt4

Myogenic microRNAs are important regulators of muscle development and differentiation. To better understand the roles of chromatin-modifying and remodeling enzymes in the activation of myogenic microRNA expression, we have functionally analyzed two different protein arginine methyltransferases, Prmt5 and Prmt4, both of which have previously been implicated in the regulation of myogenic mRNA expression. Both Prmts are required for myogenic microRNA induction during differentiation. Prmt5 is indirectly required due to the necessity of Prmt5 for expression of the transcriptional regulator, myogenin, as ectopic expression of myogenin eliminates Prmt5 dependency. By contrast, Prmt4 binds to the upstream regulatory regions of myogenic microRNAs and is required for dimethylation of the Prmt4 substrate, H3R17, at microRNA regulatory sequences. Deletion of Prmt4 does not alter MyoD binding at myogenic microRNA regulatory sequences but prevents the binding of both myogenin and the Brg1 ATPase that catalyzes SWI/SNF-dependent chromatin remodeling, resulting in an inhibition of microRNA expression.

Histone demethylase LSD1 is required to induce skeletal muscle differentiation by regulating myogenic factors

During myogenesis, transcriptional activities of two major myogenic factors, MyoD and myocyte enhancer factor 2 (Mef2) are regulated by histone modifications that switch on and off the target genes. However, the transition mechanism from repression to activation modes of histones has not been defined. Here we identify that lysine specific demethylase 1, (LSD1) is responsible for removing the repressive histone codes during C2C12 mouse myoblast differentiation. The potent role of LSD1 is suggested by the increment of its expression level during myogenic differentiation. Moreover, by performing co-immunoprecipitation and ChIP assay, physically interaction of LSD1 with MyoD and Mef2 on the target promoters was identified. Their interactions were resulted in upregulation of the transcription activities shown with increased luciferase activity. Interruption of demethylase activity of LSD1 using shRNA or chemical inhibitor, pargyline, treatment led to aberrant histone codes on myogenic promoters during skeletal muscle differentiation. We also demonstrate that inhibition of LSD1 impairs C2C12 mouse myoblast differentiation. Our results show for the first time the regulatory mechanism of myogenesis involving histone demethylase. Altogether, the present study suggests a de-repression model and expands the understanding on the dynamic regulation of chromatin during myogenesis.

β1-syntrophin modulation by miR-222 in mdx mice

BACKGROUND

In mdx mice, the absence of dystrophin leads to the deficiency of other components of the dystrophin-glycoprotein complex (DAPC), making skeletal muscle fibers more susceptible to necrosis. The mechanisms involved in the disappearance of the DAPC are not completely understood. The muscles of mdx mice express normal amounts of mRNA for the DAPC components, thus suggesting post-transcriptional regulation.

METHODOLOGY/PRINCIPAL FINDINGS

We investigated the hypothesis that DAPC reduction could be associated with the microRNA system. Among the possible microRNAs (miRs) found to be upregulated in the skeletal muscle tissue of mdx compared to wt mice, we demonstrated that miR-222 specifically binds to the 3'-UTR of β1-syntrophin and participates in the downregulation of β1-syntrophin. In addition, we documented an altered regulation of the 3'-UTR of β1-syntrophin in muscle tissue from dystrophic mice.

CONCLUSION/SIGNIFICANCE

These results show the importance of the microRNA system in the regulation of DAPC components in dystrophic muscle, and suggest a potential role of miRs in the pathophysiology of dystrophy.

Members of the microRNA-17-92 cluster exhibit a cell-intrinsic antiangiogenic function in endothelial cells

MicroRNAs are endogenously expressed small noncoding RNAs that regulate gene expression on the posttranscriptional level. The miR-17-92 cluster (encoding miR-17, -18a, -19a/b, -20a, and miR-92a) is highly expressed in tumor cells and is up-regulated by ischemia. Whereas miR-92a was recently identified as negative regulator of angiogenesis, the specific functions of the other members of the cluster are less clear. Here we demonstrate that overexpression of miR-17, -18a, -19a, and -20a significantly inhibited 3-dimensional spheroid sprouting in vitro, whereas inhibition of miR-17, -18a, and -20a augmented endothelial cell sprout formation. Inhibition of miR-17 and miR-20a in vivo using antagomirs significantly increased the number of perfused vessels in Matrigel plugs, whereas antagomirs that specifically target miR-18a and miR-19a were less effective. However, systemic inhibition of miR-17/20 did not affect tumor angiogenesis. Further mechanistic studies showed that miR-17/20 targets several proangiogenic genes. Specifically, Janus kinase 1 was shown to be a direct target of miR-17. In summary, we show that miR-17/20 exhibit a cell-intrinsic antiangiogenic activity in endothelial cells. Inhibition of miR-17/20 specifically augmented neovascularization of Matrigel plugs but did not affect tumor angiogenesis indicating a context-dependent regulation of angiogenesis by miR-17/20 in vivo.

Circulating microRNAs are new and sensitive biomarkers of myocardial infarction

AIMS

Circulating microRNAs (miRNAs) may represent a novel class of biomarkers; therefore, we examined whether acute myocardial infarction (MI) modulates miRNAs plasma levels in humans and mice.

METHODS AND RESULTS

Healthy donors (n = 17) and patients (n = 33) with acute ST-segment elevation MI (STEMI) were evaluated. In one cohort (n = 25), the first plasma sample was obtained 517 ± 309 min after the onset of MI symptoms and after coronary reperfusion with percutaneous coronary intervention (PCI); miR-1, -133a, -133b, and -499-5p were ~15- to 140-fold control, whereas miR-122 and -375 were ~87-90% lower than control; 5 days later, miR-1, -133a, -133b, -499-5p, and -375 were back to baseline, whereas miR-122 remained lower than control through Day 30. In additional patients (n = 8; four treated with thrombolysis and four with PCI), miRNAs and troponin I (TnI) were quantified simultaneously starting 156 ± 72 min after the onset of symptoms and at different times thereafter. Peak miR-1, -133a, and -133b expression and TnI level occurred at a similar time, whereas miR-499-5p exhibited a slower time course. In mice, miRNAs plasma levels and TnI were measured 15 min after coronary ligation and at different times thereafter. The behaviour of miR-1, -133a, -133b, and -499-5p was similar to STEMI patients; further, reciprocal changes in the expression levels of these miRNAs were found in cardiac tissue 3-6 h after coronary ligation. In contrast, miR-122 and -375 exhibited minor changes and no significant modulation. In mice with acute hind-limb ischaemia, there was no increase in the plasma level of the above miRNAs.

CONCLUSION

Acute MI up-regulated miR-1, -133a, -133b, and -499-5p plasma levels, both in humans and mice, whereas miR-122 and -375 were lower than control only in STEMI patients. These miRNAs represent novel biomarkers of cardiac damage.

Re-inspection of small RNA sequence datasets reveals several novel human miRNA genes

Background

miRNAs are key players in gene expression regulation. To fully understand the complex nature of cellular differentiation or initiation and progression of disease, it is important to assess the expression patterns of as many miRNAs as possible. Thereby, identifying novel miRNAs is an essential prerequisite to make possible a comprehensive and coherent understanding of cellular biology.

Methodology/Principal Findings

Based on two extensive, but previously published, small RNA sequence datasets from human embryonic stem cells and human embroid bodies, respectively [1], we identified 112 novel miRNA-like structures and were able to validate miRNA processing in 12 out of 17 investigated cases. Several miRNA candidates were furthermore substantiated by including additional available small RNA datasets, thereby demonstrating the power of combining datasets to identify miRNAs that otherwise may be assigned as experimental noise.

Conclusions/Significance

Our analysis highlights that existing datasets are not yet exhaustedly studied and continuous re-analysis of the available data is important to uncover all features of small RNA sequencing.

Small RNAs have a big impact on regeneration

A number of lower vertebrates including urodele amphibians and teleost fish are remarkably adept at repairing and regenerating damaged tissues and organs. Freshwater planarians are even more amazing, capable of regenerating entire body plans from small amputated fragments. In contrast, mammalian regenerative capacity is quite limited but of intense interest, especially related to human health and disease. For those organisms capable of robust regeneration, a common theme is the use of stem cells to replace complex tissues. Key questions remain as to the origin of these cells, whether there are pools of such cells that migrate to injured regions or whether they are generated on site. Beyond their origin, how are the genetic pathways that enable differentiation into multiple cell types and tissues regulated? microRNAs (miRNAs) are small noncoding RNAs that have recently been shown to play important roles in controlling stem cell self-renewal, proliferation and differentiation. Some of these are thought to be required to maintain "stemness". Here, we summarize recent work on the role of miRNAs in stem cells and their roles during regeneration.

MicroRNA-33 and the SREBP host genes cooperate to control cholesterol homeostasis

Proper coordination of cholesterol biosynthesis and trafficking is essential to human health. The sterol regulatory element-binding proteins (SREBPs) are key transcription regulators of genes involved in cholesterol biosynthesis and uptake. We show here that microRNAs (miR-33a/b) embedded within introns of the SREBP genes target the adenosine triphosphate-binding cassette transporter A1 (ABCA1), an important regulator of high-density lipoprotein (HDL) synthesis and reverse cholesterol transport, for posttranscriptional repression. Antisense inhibition of miR-33 in mouse and human cell lines causes up-regulation of ABCA1 expression and increased cholesterol efflux, and injection of mice on a western-type diet with locked nucleic acid-antisense oligonucleotides results in elevated plasma HDL. Our findings indicate that miR-33 acts in concert with the SREBP host genes to control cholesterol homeostasis and suggest that miR-33 may represent a therapeutic target for ameliorating cardiometabolic diseases.

MiR-322/424 and -503 are induced during muscle differentiation and promote cell cycle quiescence and differentiation by down-regulation of Cdc25A

This article describes a novel role of Cdc25A down-regulation during differentiation of proliferating myoblasts.

Induction of a G1 phase cell cycle arrest, caused primarily by the inhibition of cyclin-dependent-kinase 2 (cdk2), is a critical step in the differentiation of myoblasts into myotubes. Here, we report that two microRNAs, miR-322/424 and miR-503, are induced and promote cdk2 inhibition during myogenesis. These microRNAs down-regulate Cdc25A, the phosphatase responsible for removing inhibitory phosphorylation of cdk2, both in myoblasts differentiating into myotubes and in nonmuscle cells. Cdc25A is down-regulated during muscle differentiation by multiple pathways: action of these two microRNAs, proteasomal degradation of Cdc25A protein and transcriptional repression. Overexpression of Cdc25A or of cdk2 with mutations on T14 and Y15 (cdk2-AF), so that it cannot be inhibited by phosphorylation, decreases differentiation and differentiation-induced cell cycle quiescence. Introduction of miR-322/424 and miR-503 in heterologous cancer cells induces G1 arrest, which is also attenuated by overexpression of the cdk2-AF mutant. Until now Cdc25A and the inhibitory phosphorylation on T14 and Y15 of cdk2 have only been implicated in the intra-S phase checkpoint pathway after DNA damage. Our results reveal an unexpected role of Cdc25A down-regulation and the inhibitory phosphorylation of cdk2 T14 and Y15 in cell cycle quiescence during muscle differentiation and implicate two muscle differentiation-induced microRNAs in the process.

MicroRNAs in Head and Neck Squamous Cell Carcinoma (HNSCC) and Oral Squamous Cell Carcinoma (OSCC)

MicroRNAs (miRNAs) are small, noncoding RNAs which regulate cell differentiation, proliferation, development, cell cycle, and apoptosis. Expression profiling of miRNAs has been performed and the data show that some miRNAs are upregulated or downregulated in cancer. Several studies suggest that the expression profiles of miRNAs are associated with clinical outcomes. However, the set of miRNAs with altered expressing differs depending on the type of cancer, suggesting that it is important to understand which miRNAs are related to which cancers. Therefore, this review aimed to discuss potentially crucial miRNAs in head and neck squamous cell carcinoma (HNSCC) and oral squamous cell carcinoma (OSCC).

A view from Drosophila: multiple biological functions for individual microRNAs

microRNAs (miRNAs) comprise an extensive class of post-transcriptional regulatory molecules in higher eukaryotes. Intensive research in Drosophila has revealed that miRNAs control myriad developmental and physiological processes. Interestingly, several of the best-studied miRNAs impact multiple biological processes, often by regulating distinct key target genes in each setting. Here we discuss the roles of some of these pleiotropic miRNAs, and their implications for studying and interpreting the roles of miRNAs in gene regulatory networks.

Cloning and characterization of microRNAs from porcine skeletal muscle and adipose tissue

MicroRNAs (miRNAs) are an abundant class of small regulatory RNAs that regulate the stability and translation of cognate mRNAs. Although an increasing number of porcine miRNAs has recently been identified, the full repertoire of miRNAs in pig remains to be elucidated. To identify porcine miRNAs potentially involved in myogenesis and adipogenesis, we constructed small RNA cDNA libraries from skeletal muscle and adipose tissue and identified 89 distinct miRNAs that are conserved in pig, of which 15 were new. Expression analysis of all newly identified and selected known porcine miRNAs revealed that some miRNAs were enriched in a tissue-specific manner, whereas others were expressed ubiquitously in the porcine tissues examined. Our results expand the number of known porcine miRNAs and provide useful information for further investigating the biological functions of miRNAs associated with growth and development of skeletal muscle or adipose tissue in pig.

Mir-214-dependent regulation of the polycomb protein Ezh2 in skeletal muscle and embryonic stem cells

Polycomb group (PcG) proteins exert essential functions in the most disparate biological processes. The contribution of PcG proteins to cell commitment and differentiation relates to their ability to repress transcription of developmental regulators in embryonic stem (ES) cells and in committed cell lineages, including skeletal muscle cells (SMC). PcG proteins are preferentially removed from transcribed regions, but the underlying mechanisms remain unclear. Here, PcG proteins are found to occupy and repress transcription from an intronic region containing the microRNA miR-214 in undifferentiated SMC. Differentiation coincides with PcG disengagement, recruitment of the developmental regulators MyoD and myogenin, and activation of miR-214 transcription. Once transcribed, miR-214 negatively feeds back on PcG by targeting the Ezh2 3'UTR, the catalytic subunit of the PRC2 complex. miR-214-mediated Ezh2 protein reduction accelerates SMC differentiation and promotes unscheduled transcription of developmental regulators in ES cells. Thus, miR-214 and Ezh2 establish a regulatory loop controlling PcG-dependent gene expression during differentiation.

Molecular and cellular biology of rhabdomyosarcoma

Rhabdomyosarcoma is a group of soft-tissue sarcomas that share features of skeletal myogenesis, but show extensive heterogeneity in histology, age and site of onset, and prognosis. This review matches recent molecular data with biological features of rhabdomyosarcoma. Alterations in molecular pathways, animal models, cell of origin and potential new therapeutic targets are discussed.

Meta-regulation: microRNA regulation of glucose and lipid metabolism

Maintenance of homeostasis during environmental flux requires constant metabolic adjustment, achieved partly through the fine regulation of gene expression. MicroRNAs are key players in this regulatory milieu; they have been implicated in regulating gene expression within several metabolically active tissues including the endocrine pancreas, liver and adipose tissue. Recent studies, for example, implicate miR-375 in pancreatic islet cell viability and function, and removal or overexpression of miR-375 profoundly affects glucose metabolism. In the liver, miR-122 is important for normal lipid metabolism. In fact, misexpression of miRNAs can occur in some diseases, suggesting that restoring miRNA expression is a potential therapeutic approach for both metabolic syndrome and diabetes.

Putative Role of MicroRNA-Regulated Pathways in Comorbid Neurological and Cardiovascular Disorders

Background. The conserved noncoding microRNAs (miRNAs) that function to regulate gene expression are essential for the development and function of the brain and heart. Changes in miRNA expression profiles are associated with an increased risk for developing neurodegenerative disorders as well as heart failure. Here, the hypothesis of how miRNA-regulated pathways could contribute to comorbid neurological and cardiovascular disorders will be discussed. Presentation. Changes in miRNA expression occurring in the brain and heart could have an impact on coexisting neurological and cardiovascular characteristics by (1) modulating organ function, (2) accentuating cellular stress, and (3) impinging on neuronal and/or heart cell survival. Testing. Evaluation of miRNA expression profiles in the brain and heart tissues from individuals with comorbid neurodegenerative and cardiovascular disorders will be of great importance and relevance. Implications. Careful experimental design will shed light to the deeper understanding of the molecular mechanisms tying up those different but yet somehow connected diseases.